1. Field of Invention
The invention generally relates to indoor and outdoor play surfaces for games and activities, especially where a ball is used. More particularly, the invention relates to tennis court surfaces that include cullet obtained from waste glass.
2. Description of the Related Art
Early athletic surfaces, particularly tennis court surfaces, were constructed from concrete, grass, asphalt or clay. Each of these surfaces has significant deficiencies. Clay surfaces, which strictly speaking are only those surfaces utilizing natural clay (i.e., naturally occurring hydrated silicate materials), are soft and easy to play on. However, clay surfaces are expensive to install, difficult to maintain, and must be closed after the first frost in cold climates. Asphalt and concrete are unyielding surfaces that frequently cause injuries. In addition, concrete and asphalt surfaces, when exposed to extremes of heat and cold and to water and ice, often crack or split, thus making them less useful and subject to constant repair. Moreover, grass wears badly with frequent use and is difficult to maintain in good condition when the weather is very hot or cold.
Due to longer life spans and an increasing emphasis on keeping up physical activity later in life, attention has recently re-focused on providing play surfaces that tend to minimize stress to joints and injury in general. Thus, giving yet resilient clay-like surfaces have been developed for use on tennis courts, as well as for track and field and other athletic play applications, in the hopes of providing a cost-effective surface composition that reduces injuries. However, since economy is still a primary concern, alternatives to the traditional clay play surfaces must ideally still be low cost, inexpensive to maintain, and able to be used in varying weather conditions.
One improved clay-like product is sold under the trademark Classic Clay. Classic Clay is reddish maroon or green in color and is a manufactured, polymer-coated silica. It is filled into a carpet of specified height and is piled over the top of the carpet by about 2 mm. Classic Clay has a static charge, which causes the particles to cling to tennis balls, clothing and shoes. In terms of play characteristics, surface speed is moderate and Classic Clay is hydrophobic, meaning it does not mix well with water, and, thus, provides good playability when moist. However, Classic Clay stains tennis shoes and accessories a reddish color.
Naturally existing sand is another alternative. Natural sand is tan or grayish in color (similar to beach or playground sand) or, when crushed brick is added, pinkish in color. Sand used in tennis courts typically exists as a 6.5-9 cm compacted layer on top of 7.6 cm of compacted aggregate, with fines further compacted on rolled local soil. The play is quite slow with a great amount of sliding. Moreover, while sand courts require regular irrigation to saturate the surface, they cannot be played on when truly wet, such as after a moderate rain.
Another clay-like product is called Har-Tru. Har-Tru is a trademark for a bluish green to light blue in color product made from mined and modified shale and slate. Har-Tru American Red is crushed red stone and crushed red brick. Neither contain a binder to aid in draining. Generally, Har-Tru courts are kept moist to improve surface performance, which can result in a high maintenance bill. While the overall construction is similar to courts made with natural sand, many desirable options, such as built-in irrigation and lining, can make construction quite costly. Play is rather slow, with minimal sliding. However, Har-Tru courts can be slippery after a rain.
Other “alternative” athletic play surfaces for clay-like running tracks, tennis courts, bocce fields and the like have also included resilient synthetic plastic materials or other types of resins laid over the ground or concrete. These plastic or resinous materials, such as the products sold under the trademark “Astroturf,” have enjoyed significant commercial success. However, they also tend to be relatively expensive to install and provide a play surface that is thought to increase the risk for certain types of knee and foot injuries. Moreover, many of these surfaces are unsuitable for tennis and ball sports. This holds true even for improved plastic surfaces. For example, U.S. Pat. No. 4,307,879 by McMahon et al. describes an athletic surface made from a glass-fiber reinforced resinous material. While this material may exhibit improved characteristics for running applications, its bounce and spin characteristics appear to be incompatible with ball sports such as tennis. Hence, those in need of an athletic surface for running and ball sports have returned to examining variations on more traditional athletic surface compositions.
Accordingly, clay courts and clay-like surfaces are again coming into favor, particularly by older athletes. This is because clay and clay-like compositions are characterized by a soft, spin receptive surface that induces slow play in ball sports and helps to reduce player injuries. For example, in the context of tennis, soft courts are 10% of the $400 million U.S. court market. These courts are designed as either compacted clay-like surfacing material or surfacing material placed in a carpet, with the latter usually referred to as synthetic clay or in-fill courts. The market for these non-hard courts is increasing each year and projections indicate that the aging “baby boomers” will create continued increases in demand. In fact, all the newer clubs in traditional retirement localities, such as the Palm Springs area of Calif., have soft courts. In Arizona, several clubs in the Tucson and Phoenix metropolitan areas are replacing their hard courts with soft clay or clay-like courts.
New surfacing material must be added each year to “soft” playing fields (e.g. tracks, bocce fields) and tennis courts—leading to a substantial annual market. Because most courts and tracks are still of the so-called “hard surface” (e.g., concrete and asphalt) type, market growth is not projected to plateau for decades. Taking recent projections relating to clay or clay-like tennis courts in Australia as an indication of growth, soft court surface popularity will overtake other surface use in the coming years, with approximately 75% of the new courts using silica in-fill. In turn, each in-fill court uses approximately 10 tons of clay or clay-like material initially and 300 pounds for maintenance per year.
Due to the large amount of granular material used in various clay or clay-like compacted or in-fill athletic surfaces, manufacturers and those who maintain such surfaces are constantly looking for inexpensive alternatives. Thus, there continues to be a need for an inexpensive, widely available, and inert material for use in the manufacture and maintenance of clay and clay-like athletic surfaces.